feat(generate-config): add overwrite flag and change default env file

[rkpattnaik780]

The default file to save configuration details in environment variables has been changed from rhoas.env to .env
A --overwrite flag has been added to warn of already existing file.

Verification Steps

1. The following command should save connection configurations in a .env file:

rhoas generate-config --type env

2. Running the command again should throw the following error:

File `.env` already exists. Use --overwrite to overwrite the file, or the --output-file flag to choose a different location.

3. The existing file can be overridden using the --overwrite flag.

rhoas generate-config --type env --overwrite

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation change
• Other (please specify)

[wtrocki]

Suggested change

	one = 'file {{.FilePath}} already exists. Use --overwrite to overwrite the file, or the --output-file flag to choose a different location'
	one = 'file {{.FilePath}} already exists. Use --overwrite flag to overwrite the file, or the --output-file flag to choose a different location'

[wtrocki]

Suggested change

	one = 'Forcibly overwrite a configuration file if it already exists'
	one = 'Overwrite a configuration file if it already exists'

[wtrocki]

CC @jackdelahunt for verification

[jackdelahunt]

@rkpattnaik780 Looks good to me 👍